Flexible polyurethane foams are generally prepared by reacting an organic polyisocyanate and a polyol in the presence of a blowing agent, a catalyst, and a foam stabilizer. Typical polyols used in the art include polyether polyols prepared by alkoxylating an hydroxy-functional initiator. While foams prepared from these polyols are satisfactory for many applications, such foams may not be firm enough for several applications. Firmer foams can be produced by using polymer polyols prepared by polymerizing one or more ethylenically unsaturated monomers in a polyether polyol; dispersions of polyureas and/or polyhydrazodicarbonamides in hydroxyl group containing materials (see e.g. U.S. Pat. Nos. 4,042,537 and 4,089,835); higher functionality initiators, short chain crosslinkers (see, e.g. U.S. Pat. Nos. 3,067,148 and 3,948,825) and/or fillers. However, these solutions lead to other deficiencies such as processing difficulties.